This project proposes to demonstrate any difference in activity of the superficial and deep layers of the masseter and temporalis muscles correlated with different phases of the masticatory stroke and biting force. It will determine whether or not the human inferior belly of the lat. pterygoid contracts on jaw depression and the superior belly contracts on jaw elevation as demonstrated in the Rhesus monkey. It will also demonstrate the pattern of lat. pterygoid and inferior belly activity during dysfunction of the TMJ meniscus, i.e., meniscus-condyle discoordination with joint records.